A common mechanism for locking a shaft against rotation relative to a structural ground includes a pawl coupled to the structural ground and biased for radially directed insertion into a gap between two gear teeth on the shaft, wherein the pawl to radially engages one gear tooth on the shaft. A disadvantage of this type of locking mechanism is that it requires a radially directed load on the pawl that is transmitted through the shaft and opposed by the rotary bearings supporting the shaft. These loads may reduce the reliability of the components within the locking mechanism. Another disadvantage is that the pawl is not always in line with a gap between two gear teeth, so it is not always in proper alignment for full locking engagement. The shaft must continue to rotate until proper alignment is achieved, or the single radially engaging pawl might sit on the tip of a tooth, thereby giving false indication of a full lock.
It is also known to provide an automatic engagement device, for example a Bendix drive “twisting” clutch, whereby a tooth that is fixed rotationally relative to structural ground is axially pushed into meshing engagement with a gear on the rotating shaft. This type of locking mechanism has the problem that the gear on the rotating shaft will sometimes rotate around with the re-indexing nature of the Bendix action and not go into meshing engagement with the rotationally fixed braking tooth.
Another common mechanism for locking a shaft against rotation relative to a structural ground is an axially sliding spline configured to lock all of the teeth on the rotating shaft at once, or an axially sliding clutch-half configured to mate with a corresponding clutch half on the shaft. Examples of axial coupling mechanisms include a synchromesh clutch, a Bendix clutch, and a face gear clutch. The synchromesh clutch uses a sliding collar which is pushed axially to lock two shafts together. A Bendix clutch has a helical screw alignment device for axially pushing a fixed tooth into meshing engagement with a rotatable gear on the rotating shaft. A face gear clutch has teeth or dogs on the face of two clutch halves that mesh when the two clutch halves are pushed axially together. A disadvantage of these axial engagement mechanisms is that all of the teeth are required to engage for a lock, so the shaft might continue to rotate relative to the axially sliding spline due to improper alignment and not engage on the first try.
What is needed is a rotary lock apparatus that guarantees positive engagement of a rotary shaft for stopping shaft rotation relative to a structural ground, and that does not result in undue loading on the mechanical components.